implement register for the database

BrianHicks · May 13, 2021 · 9f97b6d · 9f97b6d
1 parent bea41c4
commit 9f97b6d
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diff --git a/src/Datalog/Database.elm b/src/Datalog/Database.elm
@@ -1,5 +1,5 @@
 module Datalog.Database exposing
-    ( Database, empty, insert, mergeRelations, replaceRelation
+    ( Database, empty, insert, register, mergeRelations, replaceRelation
     , Relation, read, rows
     , Schema, FieldType(..)
     , Constant(..), Problem(..)
@@ -16,7 +16,7 @@ Resources:
   - <https://cs.uwaterloo.ca/~tozsu/courses/CS338/lectures/5%20Rel%20Algebra.pdf>
   - <https://www.cs.ubc.ca/~laks/cpsc304/Unit05-FormalLanguages.pdf>
 
-@docs Database, empty, insert, mergeRelations, replaceRelation
+@docs Database, empty, insert, register, mergeRelations, replaceRelation
 
 @docs Relation, read, rows
 
@@ -157,6 +157,32 @@ insert relationName row (Database db) =
                     )
 
 
+register : String -> List FieldType -> Database -> Result Problem Database
+register relationName schema (Database db) =
+    case Dict.get relationName db of
+        Nothing ->
+            db
+                |> Dict.insert relationName
+                    (Relation
+                        (Array.fromList schema)
+                        (Set.empty rowSorter)
+                    )
+                |> Database
+                |> Ok
+
+        Just (Relation existingSchema rows_) ->
+            if existingSchema == Array.fromList schema then
+                Ok (Database db)
+
+            else
+                Err
+                    (SchemaMismatch
+                        { wanted = existingSchema
+                        , got = Array.fromList schema
+                        }
+                    )
+
+
 {-| -}
 mergeRelations : String -> Relation -> Database -> Result Problem Database
 mergeRelations relationName (Relation schema newRows) (Database db) =

diff --git a/tests/Datalog/DatabaseTests.elm b/tests/Datalog/DatabaseTests.elm
@@ -147,6 +147,66 @@ readTests =
         ]
 
 
+registerTests : Test
+registerTests =
+    describe "register"
+        [ test "cannot read a relation which has not been pre-registered and doesn't exist" <|
+            \_ ->
+                empty
+                    |> read "test"
+                    |> Expect.equal (Err (RelationNotFound "test"))
+        , test "can read a relation which has been pre-registered but doesn't exist" <|
+            \_ ->
+                empty
+                    |> register "test" [ StringType ]
+                    |> Result.andThen (read "test")
+                    |> Result.map rows
+                    |> Expect.equal (Ok [])
+        , test "can read the actual rows from a field that has been pre-registered and then filled" <|
+            \_ ->
+                empty
+                    |> register "test" [ StringType ]
+                    |> Result.andThen (insert "test" [ String "test" ])
+                    |> Result.andThen (read "test")
+                    |> Result.map rows
+                    |> Expect.equal (Ok [ Array.fromList [ String "test" ] ])
+        , test "can read the actual rows from a field that has been filled and then pre-registered" <|
+            \_ ->
+                empty
+                    |> insert "test" [ String "test" ]
+                    |> Result.andThen (register "test" [ StringType ])
+                    |> Result.andThen (read "test")
+                    |> Result.map rows
+                    |> Expect.equal (Ok [ Array.fromList [ String "test" ] ])
+        , test "cannot register with the wrong schema after inserting" <|
+            \_ ->
+                empty
+                    |> insert "test" [ String "test" ]
+                    |> Result.andThen (register "test" [ IntType ])
+                    |> Expect.equal
+                        (Err
+                            (SchemaMismatch
+                                { wanted = Array.fromList [ StringType ]
+                                , got = Array.fromList [ IntType ]
+                                }
+                            )
+                        )
+        , test "cannot insert with the wrong schema after registering" <|
+            \_ ->
+                empty
+                    |> register "test" [ IntType ]
+                    |> Result.andThen (insert "test" [ String "test" ])
+                    |> Expect.equal
+                        (Err
+                            (SchemaMismatch
+                                { wanted = Array.fromList [ IntType ]
+                                , got = Array.fromList [ StringType ]
+                                }
+                            )
+                        )
+        ]
+
+
 queryTests : Test
 queryTests =
     describe "query"